Evaluation of Effect of Handle Vibration Diesel-Fueled Single-Axle Tractor on Handgrip Strength of Operators


 Background: The transmission of vibration from a single-axis tractor to the human body is determined by its dynamic response; this, in turn, depends on the physical characteristics of a person's hand, the contact area, the strength of the grip, the push force of the tractor, and the position. The purpose of this work was to measure and evaluate handgrip strength and fatigue resistance for operators of a 15 horsepower single-axle tractor before and after vibration exposure. Methods: Grip strength of dominant and non-dominant hands before and after 30 minutes of tilling operations was measured and recorded. The operators performed tilling tasks with the tractor in third gear, while the vibration levels were measured at the tractor handle along with the vertical, forward, and transverse directions. Results: The average operator grip strength was 33.6 ± 2.7 and 26.3 ± 3.3 kg and the average overall grip strength declined from 39.7 to 29.31 kg, although the average fatigue strength was 27.6 and 26.5 seconds for the dominant hand before and after vibration exposure. For the non-dominant hand, the mean grip strength measured was 28.7±2.9 and 23.1±1.9 kg and the maximum grip strength was 32.79 and 26.25, while fatigue was 29.76 and 22 seconds before and after tilling respectively.Conclusion: The average reduction in grip strength suggest considerable differences in grip strength for dominant and non-dominant hands of single axle tractor operators and shows that vibration transmitted from the single axle tractor handle has a major effect on the operators.


Background
During several hours of farming, operators of single-axle tractors are subjected to large quantities of hand vibration. Vibration feedback from most power tools to the hand contains inputs from all three orthogonal motion axes and frequency-weighted RMS acceleration values for vertical, forward and lateral direction measured as a hwx , a hwy , and a hwz are recorded separately using the frequency-weighting graph, respectively [1].
Hand-tractor coupling forces are the main quantities for calculating hand-transmitted vibration; they must be continuously measured during physiological effects studies [2,3]. According to the Gri n study [4], the vibration transmission is largely determined by the dynamic response of the hand; this, in turn, depends on the physical characteristics of the individual hand, the contact area, the grip force, the push force, the location, etc. The effect of these variables can be quanti ed by calculating the energy used by the hand instead of the vibration frequency on the tool handle. Friction forces tangential to the surface of the handle are linked to the grip strength originating from the grip contact pressure normal to the handle surface [5,6].
Long-term vibration damage from vibratory equipment results in muscle fatigue affecting grip strength [7] and research performed on different occupational groups, such as cleaners, dental hygienists, dental technicians, dentists, drivers, metalworkers, and wood product assemblies, suggested that the most common symptoms were numbness and loss of grip strength [8].
Grip strength can be used as a quantitative measure of the e ciency of the sensor motor capacity of the user; it also serves as an indication of the applicability of the device to the task. Schlüssel et al. [9] described the grip strength as an integral part of the contact pressure over the entire hand and the contact surface; it was noted that the subject received increasing attention from industrial engineers and ergonomics researchers.
Research has shown that on average individual maximal handgrip strength is associated with anthropometric indicators such as gender, age, body weight, dominant hand, hand length, and hand width [10,11] and the transfer of vibration energy to the hand is primarily in uenced by the contact forces between the hands and the gripping zones.
In addition to the direct increase in hand vibration level with grip strength; the muscle tension causes phase shifts in the vibration [12][13][14]. Hewitt [15] has shown that vibratory tool operators such as impact hammers, grinders, and pneumatic hammers exert high grip strengths that enhance the transfer to operators of vibration energy. Research has shown that grip strength generally depends on age, with younger operators having relatively high grip strength; grip strength then decreases with age for both the dominant and non-dominant hands [16,17]. Another study [18] found that in the dominant hand, grip strength is typically higher. According to Dong et al., [19] grip strength measurements generally depend on the orientation of the measurement axis and that the maximum value can be signi cantly different from the minimum value in a given gripping action. Several studies have been conducted to nd agedependent reference (baseline) grip strength [20][21][22][23].
Workers who apply frequent forceful gripping and moving forces to vibratory tool handles may be at risk of developing circulatory, neurological, or musculoskeletal disorders. These disorders have been grouped as hand-arm vibration syndrome (HAVS). HAVS covers neurological, vascular and musculoskeletal injuries [24].
Several studies have shown that grip strength predicts upper extremity weakness and improves muscle strength, physical movement and range of motion, hand dexterity, and ability to perform day-to-day operations [25][26][27].
The strength decrement index (SDI) was de ned by Endurance [28], which is the fractional decrease in Grip Strength due to fatigue calculated by the formula: Where IS = initial Grip Strength

FS = nal Grip Strength
Of special concern is muscle fatigue arising from repeated hand surgery. With a su ciently vigorous and extended duration of exercise, the mechanical strength of the skeletal muscles decreases. Fatigue can be de ned as a progressive decline in muscle performance during exercise, or an exercise-induced reduction in the ability to exert muscle force or power [29]. In cases where the operator uses maximum force, or experiences high-frequency fatigue, the maximum grip strength available generally shows a rapid decline during work; however, there is generally a rapid recovery from this type of fatigue [29].
Several researchers [30,31]described fatigue resistance for each hand as the time for grip strength to decrease to 50% of its maximum value. Bautmans et al [32]  The MP 35 data acquisition unit (Biopac Systems Inc, USA) has four channels with sampling rates ranging from 1 to 100k samples per second and 24-bit resolution. The MP35 has an internal microprocessor to control data acquisition from the dynamometer and communication with the computer. The calibration sequence recommended by the manufacturer was used for the dynamometer before conducting the experiments.

Subjects and tasks
Seven (7)  The test method for measuring grip strength started with the dominant forearm, with a phased increase in clenches in increments of 5kg until the full grip strength was reached. Fatigue resistance speci ed as the time for maximum grip strength to decrease to 50 per cent of its initial value has also been calculated. This process was then replicated for the non-dominant forearm of all operators.

Handle vibration
During single-axle tractor operations, the mean single-axle vibration tractor was determined in vertical, forward and lateral directions for seven (7)

Grip strength fatigue resistance
For the dominant hand, average fatigue resistance for all seven tractor operators varied between 27.6 and 26.5 seconds before and after respectively ( gure 3). The corresponding fatigue resistance for the nondominant hand was 29.76 and 22 seconds before and after vibration exposure respectively.
Endurance is an important physical tness factor that needs to be taken into consideration when analyzing musculoskeletal functions. Measurements were made by 7 test subjects on mean grip strength scores before and after 30 minutes of single-axle tractor operation. The average estimated strength decrement index (SDI) was calculated according to Equation (3) from the operators' assessed grip strength before and after the single-axle tractor action and was found to be 28.6 per cent.

Grip Work
The grip work was calculated in compliance with equation (4) and was found to be 709 ± 213 and 523 ± 208 kg-s for the dominant hand in the seven test subjects before and after 30 minutes of single-axle tractor operation. Statistically, before and after the process, there is no substantial difference between the means of grip function (p = 0.15, that is, p > 0.05). However, during the tractor operation, there was a statistical mean decline in both grip power and fatigue resistance (p < 0.005).

Discussions
The In several studies [7,35,36], decreased grip strength with vibration sensitivity has also been reported, and exposure to hand-arm vibration over time results in reduced hand output [7,13,35,37].
The mean measured grip strength was assessed for seven (7) operators before and after single-axle tractor operation using Two-way ANOVA and the impact of single-axle tractor grip vibration was observed. P-values of the handgrip force of single-axle tractor operators for vibration exposure before and after single-axle tractor operation (the p-value < 0.0001, for α = 0.05) are provided in the ANOVA table (4) in column Prob>F. Vibration exposure-related handgrip strength dysfunction is a major risk factor associated with hand-arm vibration syndrome (HAVS). For all forms of vibrating devices, deterioration of handgrip power impairment may be caused by hand transmitted vibration sensitivity behaviours [38].
The results of handgrip fatigue resistance found in this research are consistent with those of Alkurdi and Dweiri, [30] who examined the relationship between handgrip strength and fatigue for various anatomical con gurations of operator work. They found fatigue resistance varied between 26.2 and 35.4 seconds for the right hand and from 23.2 to 40 seconds for the left hand.
The estimated strength decrement index (SDI) is consistent with the 23 per cent SDI value calculated for a power grip analyzer operator [28]. White et al., [39] observed a mean value of the power decrement index of 29.8 per cent in a separate test.
Deterioration of handgrip capacity is an indication of the development of musculoskeletal diseases of the upper extremity [40]. Several studies [41][42][43] have shown that workers subjected to vibratory hand tools suffer from pain, muscle weakness, resulting in musculoskeletal disorders due to diminished grip ability, fatigue, and reduced performance.
A substantial decrease in the overall grip strength measured after 30  The equivalent non-dominant hand values were 28.7 and 23.1 kg force difference of 5.6 kg (19.5 per cent) and the mean maximal grip strength declined from 32.79 to 26.25 kg, respectively, with a difference of 6.54 kg (19.95 per cent) before and after exposure to vibration. The ndings indicate a substantial average grip force difference of 7.3 and 5.6 kg, respectively, between the dominant and non-dominant hands of single axle tractor operators, and con rm that the vibration transmitted from the single axle tractor handle was greatly in uenced by the operators.

Declarations
Ethics approval and consent to participate Ethical approval was obtained from the Ethical review committee of Addis Ababa University, Ethiopia with the reference number of 1844/02/2020. The study didn't involve invasive procedures and was conformed to the Declaration of Helsinki. Following a detailed explanation about the objectives and indirect bene ts of the study, written and informed consent was obtained from each study participant. Con dentiality of the respondents was kept.

Consent for publication
Not Applicable.

Availability of data and materials
The datasets used and/or analyzed during the present study are available from the corresponding author upon reasonable request.